Our project on the control of bladder cancer has the objectives of detecting environmental carcinogens and preventing bladder cancer by protease inhibitors. We have developed sensitive colorimetric and fluorometric procedures for the assay of aromatic amines in urine. These involve the use of trinitrobenzene sulfonate and fluorescamine (Fluram). We found that four benzidine derived azo dyes are metabolically reduced in rhesus monkeys to free benzidine and monoacetyl benzidine as 1.25 percent of the dose. Benzidine itself is excreted as 1.45 percent of these two metabolites. This suggests that azo dyes are a significant hazard, especially in industrial workers. The high bladder incidence in kimono dye painters exposed to some of these azo dyes emphasizes the need for better controls. We are about to start our cancer preventive studies by injecting s.c. the protease inhibitors, Leupeptin, and Antipain into mice fed the bladder carcinogen FANFT, and by feeding the inhibitors Amcha and epsilon caproic acid to rats being fed FANFT.